What is the first line antibiotic for an uncomplicated urinary tract infection (UTI)?

First-Line Antibiotics for Uncomplicated UTI

Nitrofurantoin 100mg twice daily for 5 days is the recommended first-line antibiotic for uncomplicated urinary tract infections, followed by trimethoprim-sulfamethoxazole and fosfomycin as alternative first-line options. 1

Evidence-Based Recommendations

First-Line Options (in order of preference):

1. Nitrofurantoin (100mg twice daily for 5 days)

   • Excellent efficacy against common uropathogens
   • Low resistance rates
   • Minimal impact on gut flora
   • Contraindicated if GFR <30 mL/min 1
   • Has shown increasing use due to repositioning as first-line therapy 2

2. Trimethoprim-sulfamethoxazole (160/800mg twice daily for 3 days)

   • Traditional first-line agent 3
   • FDA-approved for urinary tract infections 4
   • Effective against E. coli and other common uropathogens
   • Consider local resistance patterns before prescribing 3

3. Fosfomycin (3g single dose)

   • Convenient single-dose administration 5
   • Good activity against resistant pathogens
   • Lower clinical and microbiological cure rates compared to nitrofurantoin 3

Second-Line Options:

1. Amoxicillin-clavulanic acid

   • Listed as first choice in WHO guidelines 3
   • Use when first-line agents cannot be used

2. Fluoroquinolones (e.g., ciprofloxacin)

   • Highly efficacious but should be reserved for more serious infections 3
   • Classified as "Watch" antibiotics by WHO due to resistance concerns 1
   • Associated with more serious adverse effects 1

3. β-Lactams (e.g., cephalexin)

   • Generally inferior efficacy and more adverse effects 3
   • Should be used with caution for uncomplicated cystitis

Important Considerations:

• Local Resistance Patterns: Consider local resistance rates, particularly for trimethoprim-sulfamethoxazole 3, 6
• Patient Factors: Consider allergies, pregnancy status, and renal function
• Antibiotic Stewardship: Reserve fluoroquinolones for more invasive infections 7
• Treatment Duration: 3-5 days for uncomplicated UTIs 1
• Contraindications:
  • Avoid nitrofurantoin if GFR <30 mL/min
  • Avoid amoxicillin/ampicillin for empirical treatment due to high resistance rates 3

Algorithm for Selection:

1. For uncomplicated UTI in otherwise healthy women:

   • Start with nitrofurantoin if GFR >30 mL/min
   • If nitrofurantoin contraindicated → trimethoprim-sulfamethoxazole (if local resistance <20%)
   • If single-dose therapy preferred → fosfomycin

2. If first-line agents contraindicated:

   • Consider amoxicillin-clavulanic acid or oral cephalosporins
   • Reserve fluoroquinolones for patients with allergies to first-line agents or when other options are unavailable

The evidence clearly supports nitrofurantoin as the optimal first-line choice due to its continued effectiveness against common uropathogens and lower propensity for developing resistance compared to other antibiotics 2, 8.